DESCRIPTION:(adapted from applicant's abstract) This proposal will examine whether there is a developmentally sensitive period in which vestibular sensation is necessary for the "normal" anatomical and physiological maturation of postural and extraocular muscles as well as motor behavior. The ferret is an excellent model for these studies because it is born with a very immature sensory system. In order to identify the critical period, both vestibular labyrinths will be removed at postnatal day 10, 15, 28, or 60. Behaviorally, the ferret's motor activity and postural reflexes will be recorded on videotape and quantified as the animals develop for 30, 60, or 90 days. Physiologically, the investigators will measure any changes in muscle contractile characteristics such as contraction speed, force and fatigue. Anatomically the investigators will examine changes in muscle fiber type, fiber diameter, muscle fiber type distribution and changes in the proportions of myosin heavy chain isoforms that result from bilateral vestibular deficits. Their major hypotheses are that anatomical and behavioral changes do occur and that there is a sensitive time period when vestibular receptor activity is necessary for normal neuromuscular and motor development.